There has been an increase in demand in recent years for the cleanup of environmentally contaminated areas such as landfills, waste holding ponds, and storage tanks. Such waste holding sites frequently contain sludge and highly viscous semi-solids that must be removed from theses areas for treatment, processing or disposal elsewhere. The sludge and other materials contained in these sites are often toxic and potentially harmful to the environment. Many of the methods developed to treat or process such waste require a controlled and consistent feed of waste material to the processing equipment in order for the processing equipment to operate at efficient levels.
Systems incorporating vacuum equipment and piping have been used to transport viscous sludge and semi-solid waste material. However, such vacuum systems alone have been found to be insufficient for the effective transport of highly viscous material due to the inherent characteristics of such materials. Highly viscous materials resist flowing due to friction and consequently often clog intake and discharge lines of such vacuum systems. This results in delivery of the waste material in slugs, rather than in a continuous flow, and thus provides an inconsistent delivery of the waste to the intended delivery site.
Combining a vacuum system with a mechanical pump to assist in the transport of viscous sludge has been proposed. One such device is that described in U.S. Pat. No. 4,924,898 to William R. Evenson. This device proposed using a centrifugal pump attached to the sludge receiving end on the intake line of a vacuum hose. The centrifugal pump was intended to serve as a booster for the vacuum pump by pushing sludge into and through the intake line. A disadvantage associated with the system is that the centrifugal pump must be fixed at the end on the vacuum intake line so that it can be placed directly into the sludge to be transported. Locating the centrifugal pump on the intake line increases its weight and makes the intact end of the intake line heavy and difficult to manipulate.
Another method for combining a mechanical pump and a vacuum pump is that proposed in U.S. Pat. No. 4,659,293 to William R. Evenson. There a blower powered vacuum system is utilized to draw sludge to a separator so that it may fall into a sealed hopper. A horizontal axis dual cylinder alternating piston pump is securely attached to the sealed hopper. Within the sealed hopper is an oscillating elbow conduit. The elbow conduit oscillates in alternating registration and communication with the two cylinders of the piston pump to transport the collected sludge from the sealed hopper to a storage location through a discharge line in communication with the elbow conduit of the hopper. A disadvantage of this design is that highly viscous sludge or semi-solids can impede or stop the oscillation of the conduit and shut down the movement of the sludge to the piston pump. Another disadvantage is that some highly viscous materials will not flow sufficiently to the piston to allow for efficient punping. Still another disadvantage is highly viscous semi-solids can cause great wear and tear on the oscillating conduit, the piston pump and the pump motor. This wear and tear will ultimately lead to downtime on the system and additional expense due to the need for increased repair, maintenance and replacement of the system components. Another disadvantage is that the flow of material in a system utilizing a piston pump will be highly pulsed. Finally, the oscillating conduit described in U.S. Pat. No. 4,659,293 is essentially a large valve. Such a valve is disadvantageous because the materials being transported can interfere with the seating of the valve. This interference can cause damage to the system or a shut down of material flow through the system due to blockage of the valve seating by an interfering object.
Still another disadvantage of the traditional vacuum systems is that these systems cannot be utilized on their own for the delivery of material to feed process equipment unless the process equipment is also under a vacuum and the flow of air goes through the equipment. Most process equipment is not designed to hold a vacuum. In addition, storage tanks filled by traditional vacuum systems must be designed for vacuum service. This increases the cost of the storage tanks and eliminates open-air access to the tanks as they are being filled.
Consequently, a need exist for improvements in sludge transporting equipment that will provide a continuous flow of highly viscous sludge and semi-solid material for further processing or disposal at atmospheric pressure with increased efficiency and with a decrease in the maintenance and repair cost of the transporting equipment.